The mother of all Crisis Crossovers. Really: the original. Appeared as a 12-issue mini-series, lasting from April, 1985 to March, 1986.

As a child, little Marvin Wolfman wanted to do a big series where every hero in DC Comics, ever, would team up to fight a cosmic villain called "The Librarian" (hey, he was 10). Then Marvin grew up and became Marv Wolfman, the man who managed to make the Teen Titans successful.

By this time, thanks to years of Alternate Universe stories, The DCU was teeming with different worlds. There was the main universe (Earth-1), the universe of the Golden Age heroes (Earth-2), the morality-switched Mirror Universe (Earth-3)... The Powers That Be thought it was getting confusing, and turning off new readers. So, in 1985, Marv got the go-ahead to clean it all up.

So, there's a Multiverse, which is just the unified set of all the different universes. The Multiverse is guarded by a Cosmic Entity called the Monitor, whose powers are related to positive matter. But his Evil Twin, the Anti-Monitor, who guards (naturally) the Anti-Matter Universe, has discovered that his powers can increase if he destroys positive-matter universes, and proceeds to destroy the entire Multiverse. Trying to stop him, the Monitor is pushed back and knocked into a coma. Awakening, the Monitor sees that the multiverse has been cut down to just the universes we've seen before. Panicking, he gathers a group of heroes from the Earths of the remaining universes, and sends them to hold back the Anti-Monitor's minions.

Crisis is notable for being one of the first comic "events" (Contest of Champions actually came first, as well as Secret Wars, which was more of a merchandising promotion like DC's Super Powers), but also for promising "Everything you know will change! The DC Universe will never be the same!" and actually delivering. Unfortunately, for every continuity problem it fixed three more sprang up in its place, leading The DCU to become even more convoluted and cluttered than it was before as writers scrambled to fill in the gaps left by characters and universes that no longer ever existed. Indeed, the changes wrought throughout the DC Universe by Crisis were so profound that, according to some, its publication marked the end of The Bronze Age of Comic Books.

Crisis on Infinite Earths was followed by a companion volume, The History of the DC Universe, which attempted to lay out a new, concise narrative for The DCU; it's still worth a read as a snapshot of a bygone time in comics with beautiful art by George Perez.

C-List Fodder: Dozens of minor characters, from the Crime Syndicate to the Ten-Eyed Man, died. Also, averted by a lot of A List Fodder: Supergirl, Barry Allen (Flash), the original Dick Grayson (Robin), and the original Green Arrow are all among the fallen.

All the Myriad Ways: By the end of the story, all save one of the eponymous Infinte Earths are destroyed, and it just happens to (more or less) be the "real" one where most of DC's stories are set. And, therefore, the good guys are considered to have won.

They "won" in the sense that they saved at least one universe. As opposed to, say, none.

And I Must Scream: For the crime of (apparently) awakening the Anti-Monitor, Pariah has spent uncounted millennia dragged from universe to universe, forced to watch their destruction and unable to die himself. As he puts it on his first appearance, when blamed for the incoming doom:

"No... mine is not the hand which slays worlds. I can do nothing more than cry."

Between My Legs: cover of issue #8 (Barry Allen and a beaten-up Psycho-Pirate between the Anti-Monitor's legs)

Half of the panels with Harbinger in them have this.

Big Bad: The Anti-Monitor is arguably the biggest and baddest of all Big Bads. He eats universes, kills Kryptonians, wrestles the embodied Wrath of God, and battles scores of the most powerful heroes of eight universes, at once.

The Blank: The Anti-Monitor briefly causes the Psycho-Pirate to lose his face in order to bring him to submission.

Continuity Reboot: The Crisis' ending was essentially a reboot with an in-universe explanation.

Continuity Snarl: Occurs to Power Girl, The Legion of Super-Heroes, and Donna Troy, after the Crisis was over. Hawkman's Continuity Snarl came later and was only indirectly due to the Crisis—it came out of the ill-advised decision to set the Hawkworld mini-series in the present, after both the Golden and Silver Age Hawkmen were already established in Post-Crisis continuity.

Well, for some books. Other books (like the retooled Green Lantern series) remained more or less Bronze Age in tone for some years. Others (like the retooled Justice League) were considerably brighter in tone. A serious Dark Age treatment wouldn't set in for a few more years.

Also a somewhat more literal and temporary example is Killer Frost, Firestorm's archenemy, who was emotionally altered by Psycho Pirate to fall in love with Firestorm so that they could actually work together. It was temporary as was intended.

Foreshadowing: In the Who's Who guidebooks, it is said that if Kal-L, Earth-Two Lois Lane, Earth-Three Alexander Luthor, Jr. and Superboy-Prime ever returned to the surviving universe, it would mean its destruction.

Heroic Sacrifice: Memorably, Supergirl and The Flash (Barry Allen). However, following the Man of Steel reboot, Supergirl did not exist due to the "Superman was the only Kryptonian survivor" edict. Both have since been brought back, although it took 18 years for Supergirl to return and 23 for Barry, which is really impressive for a comic book death. So these stuck pretty good, considering the medium.

Last Villain Stand: The Anti-Monitor, multiple times. After his fortress and army get destroyed, he decides it's time to take on all the heroes by himself at the dawn of time. When this partially fails, he gets so angry that he essentially forgets his goal of multiversal conquest and concentrates solely on destroying Earth, slowly and painfully. And when that fails, and the heroes think him defeated, he clings to life through sheer force of will, multiple times, finally fighting a one-on-one duel in a weakened state with the original Superman.

The exception of course, is the fact that Hal Jordan does not appear at all in the main mini-series, because, at that point, he resigned from the Green Lantern Corps, and was succeeded by John Stewart. He does contribute heavily to the plot in the main Green Lantern book, but he's nowhere to be found in the twelve-issue mini-series.

Meanwhile in the Future: Harbinger is a time traveller. One of her duplicates travels back in time 45,000 years to retrieve Arion, someone the Monitor needs. Her thoughts when she arrives? "Where is Arion? The Monitor will be furious if I cannot find him in time."

Messenger of Doom: Harbinger, sent by the Monitor across the Multiverse to gather heroes and to warn them of the coming destruction of their universes. Also Pariah, though usually he comes when the universe is already in the process of being destroyed, serving more as a doomed witness.

Nice Job Breaking It, Hero: The Anti-Monitor declares that he will travel to the dawn of time to change history from the beginning. The heroes pool their resources to follow him there. After completing that nearly-impossible journey, they find the Anti-Monitor waiting for them. He then effortlessly drains them all of their powers, explaining that he actually used up all of his own power just getting there, and he was counting on them following him so he could use their power to change the universe instead. So if the heroes never traveled back in time, the Anti-Monitor would have been stranded powerless in the void before creation forever.

You'd think that at the very least, somebody like Batman would have thought to say, "Wait. If he's already traveled to the dawn of time, how come we still exist?"

This was lampshaded and mocked in one of the last issues of Quasar, a title published by DC's rival, Marvel Comics. A powerful alien being known as The Geometer wants to fix what it sees as "imperfections" in the multiverse. Quasar reasons with it that the multiverse is too big to fix one problem at a time, and tells it that it should go back before the dawn of time and fix all the imperfections before they can even begin. After it goes, Quasar mentions that either it'll be powerless to change anything and be stranded there, or the Big Bang will destroy it.

Novelization: First released in 2005, with Wolfman on writing duties, and Pérez and Alex Ross doing cover art. The story is the crisis as seen from Barry Allen's point-of-view.

Omnicidal Maniac: The Anti-Monitor, though his ultimate goal is to still rule the Anti-Matter universe after all other universes have been destroyed.

Original Generation: The Monitor and Anti-Monitor, Harbinger, Pariah, Alex Luthor, Superboy-Prime, Lady Quark, and the second Doctor Light.

Rasputinian Death: The Anti-Monitor takes the cake. After being weakened by his failed attempt to rewrite the Big Bang, he got attacked by the heroes in his home dimension. His powers were weakened further when a large portion of his anti-matter was drained out by Alexander Luthor and the energy of the star he was feeding on was absorbed by Dr. Light. After Negative Woman bound the Anti-Monitor with her burning radioactive body, everybody aside from the aforementioned three heroes started blasting him. Upon reaching full charge, Dr. Light unleashed all of the energy she had collected into a beam. The attack sent the Anti-Monitor flying right into a nearby planet, breaking his armor and burning all of his internal organs. This only knocked him out for a few minutes. When he woke up, he absorbed a large mass of his Shadow Demons to power up, shattering the planet with his energy. With a mouth blast, he seemingly killed the Earth-1 version of Wonder Woman. Unfortunately for him, the Demons, which had been poisoned by the magicians, began fighting against him. While he was suffering from the effects, Kal-L chucked a moon at the Anti-Monitor, which worked. Superboy-Prime showed up to help, but was blasted away. Seeing that his friend wasn't killed instantly by the attack, Kal-L took it as a sign that the Anti-Monitor was weakening and smashed him with two continent-sized asteroids before picking up a third equally large one and ramming him with it. This attack buried the Anti-Monitor alive on another planet and actually stopped the monster's heart, but only managed to take him down for a few seconds. He suddenly burst through the rocks, out of his armor and in his energy form, and started crushing both Kal-L and Superboy-Prime with his hands. Darkseid saved the two by channeling a beam through Alexander Luthor and knocking the Anti-Monitor into the star that Dr. Light had drained power from. That didn't even do the job, as the Anti-Monitor rushed out of the star in the form of a screaming fireball, still determined to kill Kal-L. Unfortunately for him, his essence was shattered by one final punch from the man he was trying to murder. Immediately afterwards, the pieces of his essence fell into the star, making it implode. The explosion utterly obliterated the Anti-Monitor. Of course, he returned later on.

Supergirl: Barbara, there are thousands of people out there -- without powers like mine... the police, the firemen, the soldiers -- they're all ordinary people trying to keep this world from falling apart before its time.

Running the Asylum: The later revelation that Marv Wolfman had more or less been dreaming about this since he was ten led to a lot of accusations of this (in the negative sense) being thrown around, re: The DCU being one man's plaything for his childhood fantasies. (It's worth remembering that all of the DC higher-ups at the time signed off on it, though, so any "blame" has to be shared among a number of people.)

Timey-Wimey Ball: Try not to think too hard about how all the time-fluxes work, or you'll see plotholes so big a Mack truck can drive through them. In particular, don't give too much thought to this line by Martian Manhunter: "Time must be interchanging earlier on this Earth!"

Actually, it's mathematically possible to do an infinite number of things in a finite amount of time. If it takes you half the time to destroy each universe as it did the previous universe (from growing more powerful/getting better at destroying universes) you will destroy an infinite number of universes in only twice the amount of time it took you to destroy the first.

What Happened to the Mouse?: Skeletal, Bronze-Age Brainiac leads a group of heroes to Darkseid for help, and this is his last appearance. We know that anyone who survived the Crisis remained relatively unchanged, so this Brainiac could not have become the Milton Fine Brainic. Is this version of Brainiac still out there?

History of the DC Universe #2 stated that this version of Brainiac was destroyed by the Omega Men during a failed attempt to conquer the Vegan system, possibly at some point after the Crisis. Then, it vaguely mentioned a new Brainiac was created on Earth two years of the original's death.